Infrared spectrometers, particularly Fourier transform infrared (FTIR) spectrometers, are widely used for measuring the chemical composition and characteristics of materials. In an FTIR spectrometer, infrared radiation provided by a source having a relatively broad emission bandwidth is passed through an interferometer, typically a Michelson interferometer, to modulate the beam, and then through a sample before reaching a detector. The interferometer cancels out a narrow band of the wavelengths in the beam depending on the position of a moving element within the interferometer. Canceled wavelengths are scanned across a selected portion of the bandwidth of the infrared source by the interferometer in a time varying periodic fashion. The information obtained from the detector as the interferometer modulates the beam is provided to a computer which calculates a Fourier transform on the data to determine information concerning the sample, for example, to determine an absorbance spectrum of the sample in the infrared range. This spectrum may then be utilized to identify the chemical composition of the sample.
A variety of devices using various materials have been employed to produce the infrared detectors used in FTIR spectrometers. The output signal of the detector is a time varying signal which corresponds to the time varying intensity of the infrared beam that is focused on the detector. The responsivity of virtually all infrared detectors varies as a function of the temperature of the detector itself. For certain types of detectors, such as mercury-cadmium-telluride (MCT) detectors, the detector is typically cooled down to cryogenic temperatures, e.g., by use of coolant such as liquid nitrogen, to obtain a high and stable level of sensitivity for the detector. Other types of detectors, such as DTGS detectors, are able to operate at room temperature (e.g., about 72.degree. F.) but nonetheless have responsivity characteristics that vary significantly depending on the actual temperature of the detector itself. Where the FTIR instrument is used in a "plant" or industrial environment, the ambient temperature can vary widely, up to 40.degree. C. Moreover, the detector itself absorbs the energy of the focused infrared beam, which tends to increase the temperature of the detector. It is possible to control the temperature of the optics enclosure within which the detector is contained, but forced air cooling can create vibrations and temperature gradients which adversely affect the other mechanisms in the optics enclosure. Thus, it is generally desirable to cool the detector itself by some means. While water cooling and the use of cryogenic liquids is feasible, such equipment adds significantly to the cost of the instrument, as well as imposing additional operating and maintenance burdens.
For spectrometers which are utilized in a production type environment, it is highly desirable that the components of the instrument be readily accessible and easily replaceable if necessary. Prior detectors have often been mounted semipermanently within the optics enclosure and replacement of such detectors generally requires the services of a skilled technician who is trained to replace and realign the detector.